In the 1960s, the compression hip screw was introduced, resulting in improved fixation of the proximal femur. A lag screw assembly was inserted into the femoral head, a plate was attached to the lateral femur, and a compression screw joined the two. These implants provided a more rigid structure for the patient and allowed the surgeon to compress the fractured fragments against each other thereby decreasing the time to mobility. A number of compression hip screws have been introduced for fracture fixation about the proximal femur.
Newer devices and inventions explored additions to the nail and lag screw assembly to improve the fixation and ease or eliminate the need to locate the distal screw holes. These newer devices are commonly classified as “expanding devices” and expand in size, after placement, to fill the intramedullary cavity. In these patents a mechanism is actuated deploying arms or anchor blades through the cancellous bone to contact the inner cortical wall.
Other expanding devices provide surface contact with the internal cortical wall resulting in a wedge effect. Kurth, U.S. Pat. No. 4,590,930, Raftopoulos, U.S. Pat. No. 4,453,539 and Aginski, U.S. Pat. No. 4,236,512 among others have described mechanisms which deploy or expand with a molly bolt concept. These methods are complex and difficult to retract should the nail or lag screw assembly require extraction and do not deploy through the cortical bone.
In U.S. Pat. Nos. 6,443,954 and 6,488,684, both incorporated herein by reference and shown in FIG. 1 as prior art, Bramlet describes a surgical anchor which has deployable tangs. These tangs are simple in design, internally positioned, yet easily deployed into, and if desired through, the cortical bone providing improved purchase for compression of a fracture; especially in osteogenic bone. These tangs are just as easily retracted.
The tang body and the tangs of these devices are made of one piece. The tang body, in each of these devices, is round with a leading protrusion rectangularly shaped for registering the tangs with the tang exit holes. The tangs are also triangular and the tang exit holes are circular. In production, these devices require very precise tolerances, machining and assembly which results in high costs.
What is needed in the art is a low cost surgical screw that can be made of non-complex components made from different materials or combinations of materials and using easily controlled manufacturing steps.